Hydraulic systems

ABSTRACT

In an hydraulic system a pump draws liquid from a header tank by way of an auxiliary tank which is connected to the header tank, and the discharge from the pump is fed to either tank or partly to each tank under the control of a diverter valve in order to maintain the temperature of the working liquid within desired limits.

[ Nov. 6, 1973 [56] References Cited UNITED STATES PATENTS 1,637,5968/1927 Turner........................... 123/41.1 X 2,435,041 1/1948Hild l23/41.1 2,457,618 12/1948 Wiesendanger..... 123/41.1 X 3,160,2238/1964 Kumferman 180/66 R X Primary ExaminerAlbert J. MakayAttorneyScrivener, Parker, Scrivener & Clarke [57] ABSTRACT In anhydraulic system a pump draws liquid from a header tank by way of anauxiliary tank which is connected to the header tank, and the dischargefrom the pump is fed to either tank or partly to each tank under thecontrol of a diverter valve in order to maintain the temperature of theworking liquid within desired limits.

2 Claims, 3 Drawing Figures Inventors: Peter Thomas Ward, Lichfield;

Richard Terence Smith, Trysull; Donald Siverns, Sedgley, all of EnglandAssignee: Rubery, Owen & Co. Limited,

Wednesbury, England May 27, 1971 [21] Appl. No.: 147,594

Foreign Application Priority Data May 28, 1970 Great Britain......25,657/70 180/66 R, 180/44 F, 123/4l.1 Int. 862d 11/04 [58] Field ofSearch............................ 214/392, 394; 180/66 R, 44 F;123/41.1, 41.09, 41.08, 41.01

United States Patent Ward et a1.

1 1 HYDRAULIC SYSTEMS [22] Filed:

[52] US. Cl.

PATENTEDNUV slam 3770.076

sum ear 3 HYDRAULIC SYSTEMS This invention relates to improvements inhydraulic systems employing a liquid such as oil for the transmission ofpower. I

To compensate for the effect of changes in the ambient temperature onthe viscosity of the working liquid it is usual, when working in hotweather or in a hot climate, to provide means for cooling the liquid inorder to prevent overheating and lubrication failures due to the reducedviscosity of the liquid at high temperatures. On the other hand when lowambient temperatures are experienced the increase in the viscosity ofthe working liquid leads to increased and unacceptable power losses andpossible cavitation at pump suctions.

These difficulties can be mitigated to some extent by using differentworking liquids in summer and winter, but to change the liquid requiresconsiderable time and labour, and this does not take care of the rapidvariations in ambient temperature which can be experienced.

One object of our invention is to provide means whereby the temperatureof the working liquid in an hydraulic system is maintained substantiallyconstant independently of climatic conditions.

In an hydraulic system according to our invention a pump draws liquidfrom a header tank by way of an auxiliary tank which is connected to theheader tank, and the discharge from the pump is fed to either tank orpartly to each tank under the control of a diverter valve in order tomaintain the temperatue of the working liquid within desired limits.

The header tank may comprise a radiator located in a relatively exposedposition on the vehicle or machine incorporating the hydraulic system.The auxiliary tank is preferably located in a part of the vehicle ormachine which is normally warm, as for example an engine bay, and isprovided with means such as an electric immersion heater for heating theliquid. This tank may be thermally insulated.

An embodiment of the invention is described as an example and isillustrated in the accompanying drawings, in which:

FIG. 1 is a circuit diagram for an hydraulic transmission system, I

FIG. 2 is a diagrammatic representation of the temperature sensitivediverter valve included in the system of FIG. 1, and

FIG. 3 is a sketch of a vehicle incorporating the system of FIG. 1.

One application of the hydraulic system shown is in the transmissionsystem of a vehicle for handling freight containers, known as a straddlecarrier and illustrated in FIG. 3. The vehicle has an arched .frame 25supported at each side by a set of hydraulically driven wheels 26 andcan straddle a stack of two or, in one version, three freightcontainers. At the top of the frame there is an hydraulically poweredgrappler frame (not shown) for lifting and manoeuvring a container. Aninternal combustion engine 1 on each side of the frame 25 driveshydrostatic pumps 2 and 3 which provide hydraulic fluid for a motor27drawing each wheel 26, the pumps and motors being connected in theclosed loop hydraulic circuit of FIG. 1.

In FIG. 1 the engine 1 drives variable delivery main pump 2 and abooster pump 3 which keeps the main pump primed and makes good thelosses in the system.

The booster pump 3 draws hydraulic liquid from a header tank 4 locatedhigh up on the vehicle via an auxiliary tank 5 located in the enginebay. This auxiliary tank 5 is a section of pipe which serves as ajunction for a number of hydraulic pipes leading drainage liquid frommotors and components back into the system and conveniently provides areservoir of liquid. An electric immersion heater 6 is provided in thistank for a purpose to be described.

The booster pump 3 discharges through a filter 7 having a by-pass 8 tothe suction side of the main pump 2. The main pump 2 delivers pressureliquid for the wheel motors and lifting and other hydraulic services onthe vehicle via a main hydraulic control valve 9.

Surplus liquid from the booster pump 3 is discharged through a reliefvalve 10 to the inlet of a thermostatically controlled diverter valve11. The diverter valve 11 has two outlets 12, l3,one 12 connected to theauxiliary tank 5, and the other 13 to the header tank 4. The main pump 2also discharges via the main control valve 9 and relief valve 10 to thediverter valve 1 1 when none of the services supplied by it are beingoperated.

One type of diverter valve that can be used is shown in FIG. 2. Itcomprises a body 14 having an inlet port 15 at one end the and outletports 12, 13 at the side one above the other. A hollow piston valve 16is slidable in a bore 17 in the body 14 between extreme positions inwhich one or the other of the outlet ports 12, 13 is sealed. Betweenthese extreme positions both ports may be open, the extent of theiropening being determined by the position of the piston valve 16 inrelation to these ports.

The piston 16 is connected to one part of a wax-filled thermostaticelement 18 and is biassed by a spring 19 to a position in which it sealsthe outlet port 13 to the header tank 4. The element 18 is also engagedby a separate piston 20 slidable in a bore 21 in an end cap 22 of thevalve. The position of the piston 20 is regulated by a screwed adjuster23 so that the temperature set-' ting of the element 18 is adjustable.In this position liquid discharged by the booster pump 3 is returned tothe auxiliary tank 5. As the liquid warms up it acts on the thermostaticelement which commences to expand-and moves the piston 16 so as to openthe outlet port 13 to the header tank 4. If the liquid becomes very hotthe piston 16 moves to seal the outlet port 12 to the auxiliary tank 5so that all the fluid is passed to the header tank 4 for cooling beforereturning to the auxiliary tank 5 If the vehicle is not being used, forexample overnight in very cold weather, and it is desired to maintain itin a state of readiness for use, the liquid in the auxiliary tank 5 canbe kept at a desired working temperature by the electric immersionheater 6. This insures an adequate supply of warm liquid to keep themain pump system primed, and liquid circulated by the main pump 2 isreturned mainly to the auxiliary tank 5 until the liquid in the wholesystem attains the required working temperature, as determined by thesetting of the ther- It will be appreciated that the diverter valve 11may be located elsewhere in the system. it is however convenient to haveit in a section of the system which is subjected to atmospheric pressureso that the header and auxiliary tanks 4 and 5 do not require to bepressurized. if it is desired to pressurise these tanks then thediverter valve 11 may conveniently be located in a part of the systemwhich is subjected to pressure.

It will also be appreciated that the hydraulic systems on each side ofthe straddle carrier may be interconnected and, in particular, the twoheader tanks may be connected. In vehicles or machines where it is notpractical to locate the header tank in an exposed position, the headertank may comprise a radiator with natural or forced cooling.

The system described above can be incorporated in travelling hoists forfreight containers or in any other type of hydraulically powered machineor vehicle for which it is desirable to maintain the temperature andthus the viscosity of the hydraulic fluid substantially constant.

We claim:

1. A vehicle for handling freight containers, said vehicle comprising anarched frame, a set of wheels supporting each side of the frame, andengine on each side of the frame, a main pump and a booster pump drivenby each engine, the wheels of each set being driven by pressure liquidfrom the main pump, an auxiliary tank 7 from which the booster pumpdraws liquid for supplying the suction side of the main pump, a headertank connected to the auxiliary tank means for maintaining a differencein temperature between the liquids in each tank, a diverter valve havingan inlet port connected to the discharge side of the main pump, anoutlet port connected to the auxiliary tank and a second outlet portconnected to the header tank, and a temperature sensitive elementarranged in the liquid discharged from the main pump to control theoperation of the diverter valve whereby the liquid from the main pump isdirected between the auxiliary and header tanks in accordance with thetemperature of the liquid to maintain the temperature of the workingliquid within desired limits. i i i 2. A vehicle as in claim 1 whereinthe auxiliary tank is located near the engine and the header tank islocated higher up on the frame.

1. A vehicle for handling freight containers, said vehicle comprising anarched frame, a set of wheels supporting each side of the frame, andengine on each side of the frame, a main pump and a booster pump drivenby each engine, the wheels of each set being driven by pressure liquidfrom the main pump, an auxiliary tank from which the booster pump drawsliquid for supplying the suction side of the main pump, a header tankconnected to the auxiliary tank means for maintaining a difference intemperature between the liquids in each tank, a diverter valve having aninlet port connected to the discharge side of the main pump, an outletport connected to the auxiliary tank and a second outlet port connectedto the header tank, and a temperature sensitive element arranged in theliquid discharged from the main pump to control the operation of thediverter valve whereby the liquid from the main pump is directed betweenthe auxiliary and header tanks in accordance with the temperature of theliquid to maintain the temperature of the working liquid within desiredlimits.
 2. A vehicle as in claim 1 wherein the auxiliary tank is locatednear the engine and the header tank is located higher up on the frame.